Method of and means for making coaxial cables



July 7, 1942. J. P. GITS 2,288,899

METHOD OF AND MEANS FOR MAKING COAXIAL CABLES Filed Jan. 15, 1940 2 t st 1 July 7, 1942. J. P. GITS 2,238,399

METHOD OF AND MEANS FOR MAKING COAXIAL CABLES Filed Jan. 15, 1940 2Sheets-Sheet 2 1------ IIIIIIIII'II'" Patented July 7, 1942 THOD OF ANDMEANS FOR MAKING COAXIAL CABLES Jules P. Gits, Chicago, Ill., assignorto Gits Molding Corporation, Chicago, Ill., a corporation of IllinoisApplication January 15, 1940, Serial No. 313,843

9 Claims. (Cl. 18-59) This invention relates broadly to coaxial cableconstruction and more particularly to a coaxial cable adapted especiallyfor use as a lead-in of television antennas and the like.

New eflfects are introduced in the handling of ultra high frequencywaves in television transmission and reception. Adequate pick-up atultra frequencies requires an antenna of a dipole construction havingsuch dimensions as to be tuned to the incoming signals. Fundamentally,the di-pole consists of a rod one-half wave length long. The rod is cutapart at the center, andusually a twisted pair, with one wire joined toeach halfoif the rod, is brought down to the receiving set. Care must beexercised to locate and mount the antenna in order to secure maximumsignal pick-up and avoid interference. To illustrate the difllculties ofproper reception, lack of proper signal delivery produces gray andindistinct pictures, while static interference prevents obtaining anypicture at all if the antenna is not picking up enough signal. If thesignals are weak, enough pick-up might be obtained to form a. picture,but the synchronizing impulses may not be strong enough to hold thepicture. This will cause drift, no matter how carefully the verticalhold control is adjusted. On the other hand, a slight static impulsemight cause each time a slip of one frame of the picture. One commonsource of interference is from automobile ignition. The di-pole of theantenna must be located quite often at high locations to reduce or toavoid this interference, and to prevent surrounding high buildings fromacting as larly for use as the lead-in between a television antenna andreceiver, or as the concentric tubes in television transmitting aerials,whereby to overcome the difllculties heretofore experienced, and to animproved method of making this coaxial cable whereby a very simple andeflicient structure will be provided at minimum cost.

Specifically, the invention relates to a cable structure, and a methodof making the same, that include coaxial or concentric conductors spacedfrom each other by spaced dielectric members, preferably non-absorptiveof moisture,

whereby the dielectric members together with the air chambers or pocketsformed therebetween provide an efllcient type of insulation between thecoaxial conductors and an eflicient shield against disturbances orpick-ups.

The method herein disclosed novelly includes passing the centerconductor through a die block, molding a plurality of spacers thereonand aifixing these spacers upon this center conductor by moleculartension resulting from shrinkage or contraction of the thermo-plasticmaterial employed, the spacing of these spacers themselves along thecenter conductor and the immovable afllxation thereof in this spacedrelation being advantageously accomplished preferably by a singlemolding operation. It will be understood that the outer conductor may bea single tubular or laminated member or a fabricated structure that maybe spun or otherwise placed about these spacers. The final layer orcoating of insulation may thereafter be formed about the outerconductor. If used in high frequency transmission,

a shield to the antenna. A long lead-in is therethe 011w! layer may be alead sheath or like matefore required but the signal gain may not offsetthe added resistance of the lead. To overcome this, since the lead maynot be shortened, a. coaxial cable has been suggested for the twistedpair lead. Inasmuch as the signals are received only by the horizontaldi-pole and the only purpose of a lead-in is to connect the di-pole tothe receiver, the lead-in should preferably be constructed to preventpick-up and thus avoid interference to which television apparatus isexceptionally sensitive. A poorly insulated conductor touching a metalobject may make a variable resistance contact that gives the effect ofstatic interference, or improper insulation between the conductors ofthe lead-in connecting each section of the di-pole may cause the sametrouble or pick up magnetic or radiation disturbances in the vicinity ofthe receiver.

Broadly, this invention is directed to an imrial.

It will be remembered that the method herein disclosed is noted for itssimplicity and low cost of operation, and for its ability rapidly toplace these spacer members upon the center conductor in a singleoperation, the forming operation placing these spacer members along thecentral conductor at predetermined distances and the rapid coolingthereof causing afiixation thereof in this spaced relation withoutadditional labor or other expense. The space between these members mayform sealed air pockets between the outer and inner conductors, whilethese members eifectively insulate the concentric conductors from eachother, reduce static disturbances therebetween, and prevent absorptionof any moisture that will break down this insulation.

Although the cable herein disclosed is described as being particularlyuseful as a lead-in proved type of coaxial cable adapted particubetweenthe di-poles of a television antenna and receiver and as the concentrictubes in transmitting serials, it will be understood that the cable iscapable of many uses and is not to be confined to the specific examplesgiven or to a cable necessarily having the outer conductor coaxial withthe inner conductor.

Other objects and advantages of the invention will be apparent from thefollowing detail description when takenin connection with theaccompanying drawings which form a part hereof.

In the drawings:

Figure 1 is an enlarged cross section of apertion of a coaxial orconcentric cable embodying the invention;

Fig. 2 is a view at a smaller scale of the central conductor;

Fig. 3 illmtrates the method of forming the insulatlon spacers upon thecentral conductor;

Fig. 4 illustrates the central conductor after removal from the die butbefore the trimming operation;

Fig. 5 is a transverse section through the cen ter of the die blockshown in Fig. 3;

F18. 6 is a view similar to Fig. l but illustrating a modification ofthe structure shown;

Fig. 7 illustrates a further variant embodiment of the invention;

Fig. 8 is a view similar to Fig. 3 and illustrates how the spacingmembers may be formed by a single operation upon any member of centerconductors passing through a die block at one time;

Fig. 9 illustrates a still further variant embodiment of the invention;and

Fig. 10 also illustrates a further embodiment of the invention.

The coaxial cable herein disclosed comprises an inner or centralconductor 5, an outer conductor 6 and a, plurality of spacing members 1disposed along the central conductor 5. Spacing members 1 are preferablymade of a thermo-plastic material characterized mainly by its insulationqualities and ability to be non-absorptive of moisture. I findpolystryene to be an excellent thermoplastic material for this purpose.It has excellent insulation properties which approximate those of airand has a dielectric constant of 2.6 at 60 cycles. For all practicalpurposes, this material is considered non-absorptive of moisture. Itwill be understood, however, that other materials may be used and thatpolystyrene is mentioned only as an example.

Spacing members 1 are molded directly upon central conductor 5. They arecooled upon central conductor 5 so that they will contract and therebybe aiilxed thereto in a predetermined spaced relation by moleculartension. In other words, the material of these spacing members I gripthe central conductor by molecular tension produced by contraction uponcooling. The term molecular tension to produce the afiixation of spacingmembers 1 upon central conductor 5, as I use it herein, is the resultproduced, I believe, from injecting the thermoplastic material in moltenform in die cavities as distinguished from mere heating and thensqueezing. These members 1 thereby become immovably ailixed in spacedrelation along central conductor 5 without requiring any additionaloperation or means to keep them spaced at proper distances apart.

As disclosed, the method of making the coaxial cable includes passingcentral conductor 5 through a die 8 comprising a matrix 8 and a patrixIt (Fig. 5) having a plurality of recesses orcavities ll cut thereincorresponding to the desired shape or configuration of spacing membersI. These recesses II are arranged to' communicate by pairs with passagesl2 that connect with a main passage l3 communicating with a transversepassage l4 leading to a source of supply. Each passage I2 is divided asindicated at l5 and communicates with its pair of recesses II by openinginto these recesses along one of their faces and not at their peripheraledge. Any number of recesses H may be provided in die 8 so that acorresponding number of spacing members i may be formed in one moldingoperation. The arrangement of passages l2, l3 and It may also bechanged, but I consider it advantageous to communicate with each recessII as shown so that the plastic material may be injected at one side andnot at the peripheral edge.

Fig. 3 illustrates several central conductors 5 being unrolled fromspools l6, passing through die 8 by a predetermined stepped movement andbeing rolled upon spool II with spacing members 1 formed thereon. Fig. 4illustrates a section of one of the central conductors 5 with spacingmembers 1 formed thereon as removed from die 8 following a moldingoperation. The thermoplastic material has been cooled and spacingmembers I that have been formed are fixed upon central conductor 5 inspaced relation with the usual tailings attached, these tailingsrepresenting the material'that flows into passages l2, l3 and II uponeach injection. With the material cooled or set, these are readilyremoved by being broken or severed at the point where they connect tothe sides. of spacing members 1, it being noted that the points ofconnection between each side face and the tailing is small in crosssection, and consequently, the material will break at this point withoutleaving surplus material projecting from the side faces of the spacingmembers. The cooling of the thermo-plastic material is relatively rapid.Die 8 may be suitably cooled, as by .water, so that the material may besufliciently cool when removed to permit tailings to be severed almostimmediately. In this manner, the method is continuous and spacingmembers may be molded in fixed spaced relation upon their centralconductor 5 in one operation without requining intermediate spacersbetween the members 1 or the usual tedious manual operation of threadingthe members 1 upon the central conductor with intermediate spacersinterposed or other means employed to hold members I properly spaced.

Fig. 3 illustrates how two central conductors may be passed through dieI at the same time. This permits spacing members on two conductors to beformed in one injection operation and in practically the same time aswould be required for one conductor. Die 8 may be constructed so thatany number of conductors may be passed therethrough to have spacingmembers 1 formed thereon in one injection of the thermo-plasticmaterial.

Spacing members 1 are uniform in shape and are uniformly spaced alongconductor 5, and, when inserted in outer conductor 6, their peripherywill uniformly contact the inner surface of this outer conductor so thata plurality of longitudinally spaced. air chambers 20, completely closedoff from oneanother, may be formed between these conductors along theentire length of the coaxial cable.

Outer conductor 6 may be a single tubular or laminated member throughwhich central conductor 5 is pulled with spacing members 1 formedthereon, or it may be a fabricated structure that may be spun orotherwise formed about the spacing members 7, to provide the structureshown in Fig. 1. One or more final layers or coatings of insulation 2!may thereafter be formed about outer conductor 6. If used on highfrequency transmission, the outer layer may be a lead sheath 22 or likematerial.

From the foregoing description it will be apparent that the methodherein disclosed results in forming any number of spacing members i atone time along the inner conductor of a coaxial cable in a fixed spacedrelation. This eliminates tedious and expensive assemblies that requireadditional parts which do not always assure a structure uniformly made.Moreover, the molecular tension of the thermo-piastlc material holdingthese members I in fixed relation may actually seal these members uponthe inner conductor. Air pockets are thereby provided that increase theeiliciency of the coaxial cable as a lead-in for a television receiverbecause it will prevent pick-up of undesirable signal waves andinterference disturbances produced from magnetic and radiation effects.It will be also noted that thermo-plastic material has a certain coldflow which may,. in time, advantageously form a peripheral seal betweenthe contacting edge of members i and outer conductor 6 if thiscontacting edge should fail to engage the outer conductor tightly. Ineither event, the contacting engagement will be augmented by the coldflow to assure a tight seal. Hence, moisture will not pass from one airpocket to another, and the pockets will constitute an eifective shieldagainst magnetic and radiation disturbances between the di-- poles ofthe antenna and the receiver. The omission of longitudinal spacersbetween the spacing members 1 increases the efficiency of the cablebecause the central conductor is thereby exposed to a sealed pocket ofair, which acts as a..better insulator and shield against the pick-up ofundesirable efiects along a lead-in between the antenna and receiver.

If the flexibility of central conductor 5 should cause spacing mmebers lto turn or twist when the same is inserted in outer conductor 6 or whenouter conductor 6 is spun r woven thereabout,

edge 24 of one of the die members may be cut away slightly to form asmall groove along the groove receiving the conductor. In the ejectionoperation, this groove will fill with thermoplastic material, so that,when the wire is removed from the die, a longitudinal rib 25 shown inFig. 6 is formed along conductor between spacing members I. In thismanner, conductor 5 is reinforced and the spacing members are preventedfrom twisting or turning. It will be understood, however, that spacingmembers i may be made of greater dimension along conductor 5, if sodesired, to secure a surface engagement larger than shown.

The method disclosed is exceedingly simple and inexpensive to practice.The product is likewise simple and inexpensive and may be produced at afraction of the cost of coaxial cables heretofore constructed.

It will be understood that the method of forming insulated spacingmembers I is not necessarily limited to a central conductor of a coaxialcable but may be used in other types of cables where it is desirable tospace one or more inner conductors within an outer tubular conductor.

However, the cable herein disclosed provides a very efncient cablestructure for use as the leadin between a television antenna andreceiver. The conductors thereof are effectively insulated from oneanother to prevent any pick-up of magnetic or radiation disturbances aswell as any pick-up of signal waves between the antenna and thereceiver.

I wish it to be understood, however, that central conductor 5 may becompletely surrounded by a layer 26 of insulating material, as shown inFig. 7, in order more effectively to reinforce spacing members 1 againsttwisting if there is any tendency for these spacing members to twistwhen pulled through outer conductor 6 or when this outer conductor 6 isspun or built-up upon center conductor 5 and about the spacing members.I also find this concentric layer 26 very useful to reinforce centerconductor 5 when formed of wire that is not sufiicientiy stiff to holdits shape or is of such a flexible character that it will tend to bendat or adjacent the point where it enters these spacing members, eitherthrough normal handling or when outer conductor 6 is placed about thespacing members.

When concentric layer 26 is used, the construction of the die..aciaptedto be used will be somewhat simpler. As shown in Fig. 8, grooves 22receiving center conductors 5 will be provided with a larger diameterthan the diameter of these conductors so that the molding material willflow about the center conductors lying in these grooves 21 and intorecesses it. Passages E2 and their manner of connecting to the side ofrecesses it may be eliminated. When a number of center conductorsarepassed through a single die at one time, as shown in Fig. 8, a singlecommunicating passage 28 connected to a transverse passage 29 may extendto each central conductor groove 2?. No other passage in the die isneces sary unless it is desired.

Fig. 9 illustrates another embodiment giving greater rigidity betweenspacing members i near their peripheries, which I find very effectivelyprevents any twisting of these members i and still permits the use ofair as insulation between both conductors ii and 6. In this connection,

spacing members I may be provided with strips 30 that may be preferablyformed during the same molding operation that forms the spacing members.

Fig. 10 also illustrates accomplishing substantially the same result byenlarging the area of contact between spacing members I and centerconductor 5. Although this illustration shows spacing members I as beingof diamond shape and the preceding illustrations show spacing members 1as being of disk shape, it will be.understood that other shapes may beused and are contemplated as being within the scope of the invention.

Without further elaboration, the foregoing will so fully explain thegist of my invention that others may, by applying current knowledge,readily adopt the same for use under varying conditions of service,without eliminating certain features, which may properly be said toconstitute the essential items of novelty involved, which items areintended to be defined and secured to me by the following claims.

I claim:

1. A method of making coaxial cable having a central conductor and atubular conductor coaxial with said central conductor which comprisesmolding a plurality of insulating spacing members upon said centralconductor by injecting under pressure individual bodies of molteninsulating material having greater shrinkage properties upon coolingthan said central conductor in die cavities through which said centralconductor is passed, and immovably fixing by molecular tension saidspacing members holding said central conductor in said cavities untilsaid molten material has cooled and contracted under said pressure uponsaid central conductor, and placing said central conductor with saidspacing members fixed thereon in coaxial relation within said tubularmember.

2. A method of making a coaxial cable having a central conductor and atubular conductor coaxial with said central conductor which comprisesforming along said central conductora plurality of insulating spacingmembers oi thermoplastic material having greater shrinkage propertiesupon cooling than said central conductor by molding individual bodies ofmolten material upon said central conductor in a predetermined spacedrelation, immovably aflixing by molecular tension said spacing membersin said predetermined spaced relation by the contraction of saidthermo-plastic material when cooling, and placing said central conductorwith said spacing members formed thereon in coaxial relation within saidtubular member. 7

3. A method of making a coaxial cable having aaaaaeo ation forsuccessive lengths of said central conductor, and thereafter placingsaid central conductor with said spacing members formed thereon incoaxial relation within said outer tubular conductor.

5'. A method of forming insulation spacing members upon an innerconductor disposed within an outer conductor of a coaxial cable whichcomprises moving said inner conductor through a passage within a diehaving a plurality of spaced recesses formed therein and correspondingin shape to said spacing members, injecting a central conductor, anouter tubular conductor and insulating spacing members for holding saidconductors in coaxial relation which comprises moving said centralconductor by predetermined lengths through a cooled die having aplurality of recesses therein corresponding in shape to said insulatingspacing members, injecting under pressure a thermo-plastic insulatingmaterialin a molten condition into said recesses as each length of saidcentral conductor is moved into said die to form said spacing membersthereon said thermo-plastic material having greater shrinkage propertiesthan said central conductor, and allowing the injected thermo-plasticmaterial to set and thereby become immovably aifixed by moleculartension at said recesses upon said central conductor, repeating saidoperation for successive lengths of said central conductor, andthereafter placing said central conductor with said spacing membersformed thereon in coaxial relation within said tubular conductor.

4. A method of making a coaxial cable having a central conductor, anouter tubular conductor and annular insulating spacing members throughwhich said central conductor passes for holding said conductors incoaxial relation which comprises moving said central conductor bypredetermined lengths centrally through a passage in a die and centrallythrough a plurality of recesses formed in said die and corresponding inshape to said, spacing members, injecting a thermo-plastic insulatingmaterial having greater shrinkage properties upon cooling than saidcentral conductor into said recesses at one side thereof, allowing theinjected material to set and thereby become immovably amxed by moleculartension at said recesses upon said central conductor to form saidspacing members thereon with a smooth peripheral edge, repeating saidoperinto said recesses a thermo-plastic insulating materialcharacterized by its ability to contract upon cooling and to havegreater shrinkage properties than said central conductor, and coolingthe injected thermo-plastic material to cause the same to contract andto thereby immovably amx itself by molecular tension at said recessesupon said inner conductor.

6. A method of making coaxial cables which comprises molding a pluralityof individual bodies of insulation material on one or more conductorssaid insulation material having greater shrinkage properties uponcooling than said conductors, and cooling said bodies to immovably aflixthe same by molecular tension upon said conductor or conductors.

7. A method of making coaxial cables having a plurality of separate gascontaining pockets hermetically sealed one from another which comprisesforming a plurality of spacing members of insulating material along acentral conductor by molding individual bodies of molten insulatingmaterial upon said central conductor in predetermined spaced relation,hermetically sealing said bodies of molten material upon said centralconductor upon cooling, placing an outer tubular conductorabout saidcentral conductor and said spacing members, and bringing the innersurface of said outer tubular conductor and the peripheries of saidspacing members into intimate contact with each other to provide ahermetical seal between said outer tubular conductor and said spacingmembers.

8. A method of making coaxial cables having a plurality of separate gascontaining pockets hermetically sealed one from another which comprisesforming a plurality of spacing members of insulating material along acentral conductor by molding individual bodies of molten insulatinmaterial upon said central conductor, hermetically sealing said bodiesof molten material when cooling upon said central conductor, and formingan outer tubular conductor about the peripheries of said spacing membersso as to bring the same into intimate contact with said peripheries ofsaid spacing members whereby to form a seal between the periphery ofeach spacing member and said outer tubular conductor.

9. A method of making coaxial cables having a plurality of separate gascontaining pockets hermetically sealed one from another which compriseshermetically sealing a plurality of insulation spacing members upon acentral conductor, and hermetically sealing the periphery of eachspacing member with the inner surface of an outer tubular conductor.

JULES P GITS.

